Compensating thermal relay



June 18, 1929. G. H. wHlTTlNGHAM COMPENSATING THERMAL RELAY Filed March 17, 1927 A zg/. Z-

PatentedL June 18, 1929.

GEORGE H. WHITTINGHAM, 0F BALTIMORE, MARYLAND, CONTROLLER COMPANY, 0F BALTIMORE, MARYLAND, A

LAND.

ASSIGNOR TO MONITOR `CORPORATION 0F MARY- COMPENSATING THERMAL REMY.

Application led lai-ch 17, 1927. Serial No. 176,157.-

This invention relates to a thermally operated overload relay, constructed so that the relation of the thermal device to the switch which it controls will not be affected by changes in atmospheric temperature, and the4 opening of the switch will depend solely upon the heating effect of thecurrent 1n the circuit to be controlled.

In carrying out the invention, I p rovide a switch having a member normally biased .toward closed position, a thermally responsive device controlled by a heating element., .tor moving said member to the open position, and a second thermally responsive device, afected by atmospheric temperature only, tor adjusting the position of said member, with respect to said first mentioned device, to compensate for corresponding adJustments of the latter, due to changes in atmospheric temperature.

In the accompanying drawing,

Fig. 1 is a front elevation of the compensating overload relay;

Fig. 2 is a section on the line 2-2 of Fig. 1; and, l

Fig. 3 is a top plan view of the relay..

Referring to the drawing, a and b indicate similar thermostat devices of the kind illustrated in my Patent Number 1,627,816; dated May 10, 1927, each element comprising a bimetallic band 1,. coiled helically into a tube. Brackets 2 and 3, secured to a suitable base 4 of insulating material, support the tubes at their upper and lower ends. The tubes are open at their lower ends and secured within openings in the lower arms of the brackets. A plug 5 fits into the upper end of the tube of the device a, and is secured therein. A screw 6, in the upper arm of the bracket 2, extends into a recess in the plug 5 and forms a pivot around which the plug may turn. The tube of the thermostat device b is similarly mounted. A'disk 7, of insulating material, is attached to the plug 5 and this disk extends back of a pivoted switch member c and is adapted to enga e a projection c on said member, to move t e latter. A head 8,

. secured within the upper end of the device b,

carries a laterally projecting arm 9 upon which is mounted a contact 10, and the latter is normally engaged by a contact 11 on the switch member 0. This switch member is provided with overturned ears 12, which are pivoted to a bracket 13, secured to the base 4.

A spring 14 constantly bears against one end of .the switch arm or lever and presses the other end, with its contact, against the contact of the arm of the thermal device b. The disk 7 of the device a is normally out of engagement with the project-ion c of the switch member 0.A A heating coil d extends upwardlly within() the device a, and theterminals of this coil are connected n in a circuit e, which it 1s the function of the device to protect. A

circuit f, which the relay switch directly controls, extends through the switch arm c, contacts 11 and 10, and the arm 9 of the thermostat device b, thence through said device. It will be understood that a switch g in the circuit e is normally held in closed position by a coil f in the circuit f, and that when the latter circuit is interrupted the switch will open the circuit e.

With the parts arrangedas shown in the drawing, the operation is as follows: The two thermal devices are ai'ected alike by changes in atmospheric temperature, but only one of them, the device a, is affected by the heater in the circuit e. The current in the circuit f is so small as to be negligible and it has no heating eii'ect upon the device b. The bimetallic coils of the devices a and b are wound oppositely, as shown, and, being arranged on opposite sides of the switch arm c, in the illustration given in the drawing, an increase in atmospheric temperature will causeV the insulating disk 7 and the arm 9 to move forwardly or away from the base 4, and a decrease in atmospheric temperature will cause the members to move backwardly or toward the base. As the switch arm c is constantly pressed against the Contact carried by the arm 9, the circuit through the switch will be maintained during these adjustments for atmospheric temperature, and the ldisk 7 will maintain a constant distance from the projection c on the switch arm. Thus, in extremes of atmospheric temperature, the distance between the parts 7 and c will be maintained constant, providing the tube of the device a is not heated by current in the heating device d. Wlien the current in the circuit e becomes excessive, or above a predetermined amount, for a short period, the tube of the device a uncoils and the disk 7 engages the part c and moves the switch.

cuit f, thereby de-energizing the coil f and causing the switch g to interrupt the cir cuit e.

It will be seen that the thermostat device b adjusts the switch members to compensate for changes in the position of the disk 7, carried by the device a, which may be caused,by changes in atmospheric temperature, an'd that the device a will operate to open the switch upon the occurrence of a predetermined overload current in the circuit e, without being affected by atmospheric temperature. The arm which supports the disk 7 is shorter than the arm which supports the contact 10 in the illustration given in the drawing, because these arms `are at dierent distances from the pivotal axis of the switch member c. `If the arms were arranged at the same distance from the pivotal axis of the switch member, of course, they would be made the same.length. What I claim is:

In a thermally controlled relay, two thermally responsive devices, each comprising a metal helix fixed at one en'd and havinga Ilaterally projecting arm at its opposite end, a

movable swltch member normally pressed against the arm of one of -said devices, the arm of the other device being normally out of engagement `with the switch member and adapted to engage and move said member upon predetermined rise in temperature in said latter device, arid electric heating means adjacent said latter device. i

In testimony whereof I hereunto aix my signature.

GEORGE nwmrfrmenAM. 

